Validation Popup is Clipped by DataGrid Column Header

[alexhelms]

Describe the bug A validation error popup is being clipped by the DataGrid column header. The popup is attached to a TextBox inside of a DataGrid (see below for xaml) where the TextBox is in a DataGridTemplateColumn.

To Reproduce

<DataGrid>
    <DataGrid.Columns>
        <DataGridTemplateColumn MinWidth="100"
                                Header="Exposure">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock Padding="2,0"
                               VerticalAlignment="Center"
                               Text="{Binding ImageParameters.ExposureExpression}" />
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
            <DataGridTemplateColumn.CellEditingTemplate>
                <DataTemplate>
                    <TextBox VerticalAlignment="Center">
                        <TextBox.Text>
                            <Binding Path="ImageParameters.ExposureExpression">
                                <Binding.ValidationRules>
                                    <validation:ExposureTimeValidationRule />
                                </Binding.ValidationRules>
                            </Binding>
                        </TextBox.Text>
                    </TextBox>
                </DataTemplate>
            </DataGridTemplateColumn.CellEditingTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
<DataGrid>

Expected behavior The popup should not be clipped, it should be on top of all other controls.

Screenshots